Some vehicle engine systems utilize both direct in-cylinder fuel injection and port fuel injection. The fuel delivery system may include multiple fuel pumps for providing fuel pressure to the fuel injectors. As one example, a fuel delivery system may include a lower pressure fuel pump (or lift pump) and a higher pressure (or direct injection) fuel pump arranged between the fuel tank and fuel injectors. The high pressure fuel pump may be coupled to the direct injection system upstream of a fuel rail to raise a pressure of the fuel delivered to the engine cylinders through the direct injectors. A solenoid activated inlet check valve, or spill valve, may be coupled upstream of the high pressure pump to regulate fuel flow into the pump compression chamber. However, when the high pressure fuel pump is turned off, such as when no direct injection of fuel is requested, pump durability may be affected. Specifically, the lubrication and cooling of the pump may be reduced while the solenoid activated inlet check valve of the high pressure pump is not energized, thereby leading to pump degradation. Therefore, it may be beneficial to operate the high pressure pump even while direct injection is not requested in order to maintain sufficient lubrication. During this operating condition, the high pressure pump may be adjusted to maintain a peak compression chamber pressure while not sending fuel into the direct injection fuel rail. This type of operation may be referred to as zero flow lubrication.
In one approach to implement zero flow lubrication of the high pressure pump, shown by Basmaji et al. in US 2012/0167859, closed loop (or feedback) control is used to increment duty cycle of the high pressure pump while operation of the high pressure pump is not required (zero flow lubrication). In this method, first a mass of fuel may be ingested into the pump that maintains a pressure at the pump outlet that is at or just below an estimate fuel rail pressure. Next, during closed loop control, the stroke amount of the pump may be increased intermittently. If fuel rail pressure does not increase, then the stroke amount may be further increased until a change (increase) in fuel rail pressure is detected. Alternatively, if fuel rail pressure does respond to the increased stroke, then pump operation may be decreased to a lower stroke amount such that fuel rail pressure does not respond to pump operation. As such, the approach of Basmaji et al. may attempt to compensate for variability between engines by learning high pressure pump operation during zero flow lubrication methods on-board the vehicle.
However, the inventors herein have identified potential issues with the approach of US 2012/0167859. First, while the method of Basmaji et al. may provide pump lubrication, the method may be unable to generate a full range of data that corresponds to a zero flow rate from the high pressure pump into the fuel rail. The method of Basmaji et al. provides data below or near the fuel rail pressure, but once fuel rail pressure increases pump duty cycle immediately decreases such that data may only be accrued around a near-constant, desired fuel rail pressure. Furthermore, the inventors herein have recognized that while incrementing pump duty cycle, the time before a substantially steady-state (or stable) fuel rail pressure is reached may be 10 seconds or longer. The time period to wait may be too long if a large amount of zero flow data is desired in a short amount of time.
Thus in one example, the above issues may be at least partially addressed by a method that enables faster performing of zero flow lubrication. In one example, the method comprises: while not direct injecting fuel into an engine and while the engine is in a stabilized idling condition; estimating a target fuel rail pressure based on a commanded duty cycle of a high pressure fuel pump; performing a closed loop control scheme until fuel rail pressure reaches a percentage of the target pressure; and performing an open loop control scheme until fuel rail pressure reaches the target fuel rail pressure. In this way, both open and closed loop controls may be used to accelerate the response time of the fuel rail pressure each time pump duty cycle is incrementally increased.
Furthermore, this method, also referred to herein as the rapid zero flow lubrication test, may repeatedly perform a routine that first commands closed loop control of the high pressure pump until a certain fuel rail pressure is reached, then commands open loop control until the steady-state fuel rail pressure is reached. This method may take a shorter amount of time than other methods, thereby enhancing its utility to gain a large amount of zero flow data in less time. Finally, as zero flow rate data may be plotted in order to estimate various properties such as fuel temperature, fuel composition, and fuel density, then those properties may be estimated at a faster rate than other methods.
It is noted that pump duty cycle refers to controlling the closing of the pump solenoid activated inlet check valve (spill valve), where the spill valve controls the amount of fuel pumped into a fuel rail. For example, if the spill valve closes coincident with the beginning of the engine compression stroke, the event is referred to as a 100% duty cycle. If the spill valve closes 95% into the compression stroke, the event is referred to as a 5% duty cycle. When a 5% duty cycle is commanded, in effect 95% of the displaced fuel volume is spilled and the remaining 5% is compressed during the compression stroke of the pump piston. Duty cycle is equivalent to spill valve timing, in particular the closing of the spill valve. Duty cycle is also equivalent to trapping volume fraction, or the amount of fuel that remains in the compression chamber of the high pressure pump during its compression stroke.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.